1. Field of the Disclosure
The subject disclosure relates to down-hole drilling assemblies, and more particularly to improved protection for the blades of turbine drill components.
2. Background of the Related Art
The use of generating power from a turbine system is well known and widely used in various engineering fields. In oil exploration, drilling is an established method of creating a bore-hole through the earth. Many oil exploration drilling machines are turbine drills powered by a turbine blade system. Impulse type drilling turbines are driven by a fluid at atmospheric pressure, while reaction type drilling turbines are driven by fluid pressurised to above atmospheric pressure, possessing energy which is partly kinetic and partly pressure.
The “Bernoulli principle” of creating differential pressure is used to result in a movement of the body towards the low pressure side of the body. In drilling turbine applications, the Bernoulli principle is used to transfer the hydraulic power of a drilling fluid being pumped through the drilling turbine of stators and rotors into rotational power of a rotor element, which is rigidly attached to a drive shaft system. Ultimately, the drive shaft system is connected to a drilling bit for the explicit purpose of boring through the earth's structure such as rock. The hydraulic fluid is often referred to a drilling mud.
The drilling mud usually has an abrasive component. As the mud is under pressure and potentially travels at high speed, the abrasiveness of the drilling mud erodes the internal components of the drilling turbine. The blades and adjacent support surfaces of the drilling turbine are particularly susceptible to erosion which causes poor efficiency and frequent replacement at great expense. The rate of erosion is related to fluid velocity, drilling fluid density, the shape of the internal components and the material of the internal components. By limiting the fluid velocity to avoid erosion, the speed of the drilling turbine is limited. Thus, the power density is lowered, which affects the length of the drilling tool.
The internal components are often steel of various compositions, for example, carbon steels or stainless steels. These steel materials have certain advantages and inherent disadvantages, the main advantage being that the complex shape of the blade profile is readily cast by various methods. Also, steels of certain chemical composition can be heat treated to enhance the end product characteristics. Stator and rotor elements are typically constructed as a one piece cast/moulded component or made up from several constituent parts, such as rotor blade hubs, stator blade shrouds and blades.
Despite many advances, there are still erosion problems associated with the internal components of turbine drilling due to the abrasive nature of the drilling mud.